The proposed studies are designed: (1) To investigate the metabolic basic of the recidivism exhibited so often by formerly obese patients who have successfully lost weight; (2) To identify diet(s) or procedures that may promote a successful weight maintenance and prevent the "relapse" that generally follows weight reduction; (3) to obtain a better understanding of the wide variations of metabolic responses observed in obese individuals during weight reduction induced by very low calorie diets: (4) To determine whether these different responses can be explained on the basis of types of obesity (hypertrophic vs hyperplastic) or the storage status of certain body constituents such as lean body mass or total body fat; and (5) To extend our ongoing studies of the accuracy, efficiency and convenience of new procedures (ultrasound and total body electrical conductivity) for estimating body composition and its changes.